Per the above, you don't really need any, but if you do WANT one, Clam AV is a good one. Slow, but good.

Stay away from ANYTHING Norton. Norton produces the most intrusive, problematic stuff I have ever used. It is too bad to. "Back in the day" when PCs were new and DOS ruled, Norton was absolutely required software - about the only thing that would keep your PC running. These days, Norton has become bloatware, just like the Window OS which it purports to keep safe.